A continuously variable transmission (CVT) is an uninterrupted transmission system commonly for use in transmission of motorcycles such as scooters. The CVT can be configured to provide a manual-operation mode in which users can carry out manual transmission. However, manual down transmission carried out by users in the manual-operation mode of the CVT is confronted with an increase in speed ratio, which in turn requires a great engine brake; as a result, motorcycles moving on roads with low coefficients of friction or turning are likely to trip.
Therefore, the manual-operation mode of the CVT of motorcycles poses a risk regarding driving safety.